Hydrophilic polyethersulfone membrane and method for preparing same

ABSTRACT

The present disclosure relates to improved efficient and effective systems and methods of manufacturing hydrophilic polyethersulfone (PES) membrane suitable for commercial applications and the resultant hydrophilic polyethersulfone (PES) membrane suitable for commercial applications produced thereby and includes methods of manufacturing hydrophilic polyethersulfone (PES) membrane comprising the acts of: providing hydrophobic PES membrane; prewetting the hydrophobic PES membrane in a sufficient amount of a liquid having a sufficiently low surface tension; exposing the wet hydrophobic PES membrane to a sufficient amount of an aqueous solution of oxidizer; and after the exposing act, heating the hydrophobic PES membrane for a sufficient time at a sufficient temperature and methods of manufacturing hydrophilic polyethersulfone (PES) membrane comprising the acts of: providing gel PES membrane; exposing the gel PES membrane to a sufficient amount of an aqueous solution of oxidizer; and after the exposing act, heating the hydrophobic PES membrane for a sufficient time at a sufficient temperature and the resulting products.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. ProvisionalApplication No. 60/618,522, of Mezhirov et al., filed on Oct. 13, 2004,the disclosure of which is herein incorporated by reference to theextent not inconsistent with the present disclosure.

BACKGROUND OF THE DISCLOSURE

The present disclosure relates to an improved efficient and effectivemethod of manufacturing hydrophilic polyethersulfone (PES) membranesuitable for commercial applications and the resultant hydrophilicpolyethersulfone (PES) membrane suitable for commercial applicationsproduced thereby.

As is known, PES membranes are naturally hydrophobic. Most membraneapplications require the use of hydrophilic membranes. Several differentmethods are known to transform hydrophobic PES membranes intohydrophilic PES membranes (to perform membrane hydrophilization). Someof these methods are complicated and expensive, while others fail toprovide high purity membrane (for example, the membranes could containthe remains of hazardous monomers, used for hydrophilic coating).

Several different prior known methods of PES membrane hydrophilizationare presented in the patent and scientific literature. In one knownprior method, the hydrophilization of PES membrane was accomplished bycoating the hydrophobic membrane with a hydrophilic polymer. In order toprovide the desirable permanent attachment of the hydrophilic polymer tothe membrane, a hydrophilic coating layer was usually subjected to across-linking reaction or a coating polymer was grafted to the surfaceof the hydrophobic PES membrane. The preceding approach has beendisclosed in the following patents and publications:

U.S. Pat. No. 4,618,533 disclosed a method of PES membranehydrophilization by direct membrane coating. As described, thehydrophobic membrane was prewetted with alcohol, and then soaked inaqueous solution that contained a hydrophilic monomer, a polyfunctionalmonomer (cross-linker) and an initiator of polymerization. The monomerand cross-linker were then polymerized using thermal or UV initiatedpolymerization, which formed a coating of cross-linked hydrophilicpolymer on the membrane surface.

U.S. Pat. Nos. 6,193,077 B1 and 6,495,050 B2 proposed coating the PESmembrane by soaking the membrane in an aqueous solution of hydrophilicpolymer (polyalkylene oxide) and at least one polyfunctional monomer(cross-linker), then polymerizing a monomer. As described, anon-extractable hydrophilic coating was the resultant.

The article “Surface modification of Poly(ether sulfone) UltrafiltratonMembranes by Low-Temperature Plasma-Induced Graft Polymerization(Journal of Applied Polymer Science, Vol. 72, 1699-1711 (1999))describes the hydrophilization of PES membrane by a grafting reaction.In this process as described therein, hydrophilic PES membrane wassubmitted to low-temperature helium plasma treatment followed by thegrafting of hydrophilic monomer N vinyl-2-pyrrolidone onto the membranesurface.

In another known prior method, the hydrophilization of PES membrane wasaccomplished by dissolving hydrophobic PES polymer in a solvent andblending it with a hydrophilic additive, which was soluble in the samesolvent. The obtained blended solution was used for casting ahydrophilic membrane.

The following patents disclose representative prior methods of PESmembrane hydrophilization by blending PES polymer with hydrophilicadditives.

U.S. Pat. No. 4,943,374 proposed to blend PES in a solution withhydrophilic polymers (polyethylene glycol, PVA, polyacrylic acid,polyvinilpirrolidone, etc.). According to the patent, the resultantmembranes obtained from the blended solutions were hydrophilic.

U.S. Pat. No. 6,071,406 disclosed the production of hydrophilic PESmembranes by blending PES in a solution with a wetting agent (a blockcopolymer having hydrophilic and hydrophobic units). In the resultantmembrane, the hydrophobic units of the block copolymer were permanentlyattached to the hydrophobic matrix (PES) leaving the hydrophilic unitson the membrane surface. Since, according to this patent, the wettingagent was permanently attached to the membrane and could not be leached,the resultant membrane possessed permanent hydrophilicity.

U.S. Pat. No. 5,178,765 disclosed the hydrophilization of PES membraneby blending PES with hydrophilic poly-2-oxazoline resin andpolyvinylpyrrolidone resin. According to this patent, the membraneobtained thereby exhibited long-term water wettability.

U.S. Pat. No. 6,495,043 B1 disclosed a method for PES membranehydrophilization by blending PES with hydrophilic ethyleneoxide/propylene oxide copolymer. According to this patent, the resultanthydrophilic membrane had a reduced tendency toward fouling. As is knownto those skilled in the art, the term “fouling” means clogging themembrane pores during the filtration process.

U.S. Pat. No. 6,039,872 disclosed a method of producing hydrophilic PESmembrane by blending the PES with a hydrophilic monomer and an initiatorfor thermal polymerization. After blending, the polymer solution washeated to a temperature sufficient to start a polymerization of theblended monomer. The resultant polymer solution reportedly contained ablend of PES with hydrophilic polymer. The membrane produced from thisresultant solution was reportedly hydrophilic.

U.S. Pat. No. 4,964,990 disclosed a method, which included a combinationof blending PES in a solution with a hydrophilic additive, followed by ahydrophilic coating of the membrane. In the method described in thispatent, the PES was mixed in a solution with a hydrophilic polymer(polyethylene glycol or polyvinylpyrrolidone), and then the membrane wascast, quenched and dried. The dried membrane was post treated with anaqueous solution of polyvinyl alcohol and then cross-linked. The patentclaimed that the resultant membrane possessed permanent wettability andstability after exposure to prolonged treatment in isopropanol orextended heat treatment.

In yet another known prior method, the hydrophilization of PES membranewas accomplished by treatment with low temperature plasmas. Thefollowing publications describe the application of plasma reactions forPES membrane hydrophilization:

The dissertation “Surface modification of porous polymeric materialsusing low-temperature plasmas” (Michelle L. Steen, Colorado StateUniversity, 1994) described a surface modification of several membranesfrom different polymers, including PES. To impart permanent hydrophilicproperties to these membranes, the membranes were treated withlow-temperature plasma. It was reported that the plasma treatmentinitiated formation of hydroxyl radicals (OH radicals). OH radicals werethe primary reactive species involved in membrane modification. Becauseof the influence of OH radicals, the oxidation reaction occurred, andhydrophilic groups containing oxygen appeared on the membrane surface.It was reported that the presence of these polar groups made themembrane hydrophilic.

The article “Modification of porous Poly(ether sulfone) Membranes byLow-Temperature CO₂ Plasma Treatment” (Journal of Polymer Physics, Vol.40, 2473-2488 (2002)) described the hydrophilic modification of PESmembrane by treatment with low temperature CO₂-plasma. The articleclaims the formation of hydrophilic functionalities on the membraneprimarily during a plasma treatment, with some incorporation ofatmospheric oxygen and nitrogen on the membrane surface immediately uponexposure the membrane to air.

Shortcomings of the above described prior methods are presented below.

The Coating Methods of PES Membrane Hydrophilization

One shortcoming of the above described membrane coating processes istheir degree of complexity. One representative typical scheme formembrane coating is illustrated in FIG. 1. As shown, the hydrophobic PESmembrane 10 is prewetted in an alcohol solution 12, then washed withwater 13, and soaked 14 in aqueous solution containing a hydrophilicmonomer, cross-linker (polyfunctional monomer) and the initiator ofpolymerization. Then, the thus treated membrane is sandwiched betweenfilms 16 (usually Mylar films) and proceeds to the polymerization area15. As is known, the polymerization process can be initiated by heat, UVradiation or γ-radiation. In case of thermal polymerization, themembrane typically traverses along the surface of a hot plate 15, andthe polymerization reaction is initiated at the temperature of about 80°C. to about 90° C. In cases where the reaction is initiated by UVradiation or γ-radiation, the sources of UV or γ-radiation are installedinstead of a hot plate 15, as would be appreciated by those skilled inthe art. After polymerization, the membrane is washed with water at 17and dried by conventional means at 18.

The above representative scheme shows that the coating process requiressignificant amounts of the equipment and consumes a considerable amountof Mylar film. At the same time, the monomers and the cross-linkersapplied in the representative coating polymerization process areregarded to be hazardous substances. The possibility that small amountsof these substances remain in the membrane could be a concern for themembrane applications in the fields, which require highly pure endproducts. Thus, it is clear that there is a need to significantly reducethe complexity and the cost of the membrane hydrophilization process, aswell as the possibility of hazardous substances remaining in the endmembrane product.

Blending PES with Hydrophilic Additives Methods of PES MembraneHydrophilization

The main disadvantage of this approach is that in order to achieve thedesired hydrophilization effect, the amount of applied hydrophilicadditive is usually very significant.

The following patents illustrate the amounts of hydrophilic additivesrequired to effectively practice this method. Specifically, U.S. Pat.No. 5,178,765 shows that the amount of hydrophilic polymerpoly-2-oxazoline resin blended with PES in solution is from 24 to 47% ofthe PES weight. U.S. Pat. No. 6,071,406 shows that the amount ofhydrophilic block-copolymer, blended with PES, is from 250 to 350% ofthe PES weight. U.S. Pat. No. 6,495,043 B1 shows that the amount ofhydrophilic additive (ethylene oxide/propylene oxide copolymer) is 80%of the PES weight. The presence of large amounts of the additive in themembrane (and, correspondingly, reduced amount of PES) can reduce thevaluable properties of PES membranes (such as a high stability in acidicand basic media, mechanical strength, thermal stability etc.)

Treatment of PES Membrane with Low-Temperature Plasma

The study of the treatment of PES membranes with low temperature plasmawas performed, primarily, using small laboratory reactors, as would beunderstood by those skilled in the art. In the scale-up of thelaboratory process, the plasma treatment of the membranes may cause someproblems: the process uniformity and membrane quality produced by largereactors have not always proven to be sufficient; sometimes plasma candamage the membrane due to the etching from ion bombardment. In manycases, such plasma treatment processes require a reduced pressureenvironment. These process control problems are especially importantwhen membrane manufacturing is performed as a continuous process.

Generally, although the continuous hydrophilization of PES membranes bytreatment with low-temperature plasma looks promising, currently thetechnology and the equipment for this process are in the research anddevelopment stage. Additional study will be required to reach a moredefinite conclusion about the practical application of the lowtemperature plasma approach in PES membrane manufacturing.

Additional Membrane Oxidation Prior Art

U.S. Pat. No. 4,943,373 describes and claims a hydrophilic membraneformed from polyvinylidene fluoride (PVDF) wherein hydrophilicproperties were imparted to the membrane by oxidation through thechemical treatment. Oxidation was performed through the treatment ofPVDF membrane with a strong alkali solution (10 to 60% NaOH) containingan oxidizing agent (potassium permanganate). According to the processdescription, under the action of strong alkali, conjugated double bondsare formed on the polyvinylidene fluoride as the consequence of theremoval of hydrofluoric acid from the PVDF molecule, such formed doublebounds are instantaneously oxidized producing hydrophilic polar groups.The double bond formation under the action of strong alkali is specificfor PVDF molecules. This patent describes and claims only hydrophilicoxidized membrane that can be reacted in alkali condition to formconjugated double bonds, such as PVDF. It does not include the oxidationof any membrane that cannot form conjugated double bonds in alkalicondition, such as PES membrane.

Several patents and publications describe the modification of PESmembranes by oxidation but for purposes other than hydrophilization. Thegoals of the oxidation treatments described therein did not relate tomembrane hydrophilization, and no information about change of themembrane's hydrophilic properties was presented therein.

U.S. Pat. No. 5,409,524 discloses a method for treatment of gasseparation membranes made from different polymers (including PES). Thetreatment included: a) heating the membrane at 60 to 300° C., b)Irradiating the membrane with a UV radiation source in the presence ofoxygen for a time sufficient to surface oxidize the membrane. Thetreated membranes exhibited enhanced selectivity in gas separation andno information about changes of the membrane's hydrophilic propertieswas presented therein.

Japanese Patent No. 137,487/83 discloses a process of regeneration ofspent membranes from different polymers (including PES) with the aqueoussolution containing a surfactant and an oxidizing agent (hypochloriteion or hydrogen peroxide) in order to speed up the membrane regenerationprocess. The degree of a regeneration of spent membranes in the presenceof an oxidizer was more complete (93.3%) than in the case when nooxidizer was used (66.7%); however, no information about changes of themembrane's hydrophilic properties was presented therein.

The dissertation “Microfiltration of Apple Juice: Membrane Structure andFoulant Morphology Effects on Flux Resistance” ((Kenneth M. Riedl,University of Guelph (Canada), 1996)) describes the study of membranefouling during the process of apple juice filtration. Several membranesfrom different polymers (including PES membrane) were studied. It wasshown, according to the dissertation, that resistance of a foulinglayer, formed on the membrane during a juice filtration, could bereduced by a treatment of the membrane with the oxidizing agent and noinformation about changes of the membrane's hydrophilic properties waspresented therein.

Thus, there remains a need to develop a relatively simple, costeffective and reliable method for the preparation of hydrophilic PESmembrane.

SUMMARY OF THE DISCLOSURE

One aspect of the present disclosure includes an improved method ofmanufacturing hydrophilic polyethersulfone (PES) membrane of the presentdisclosure comprising the acts of providing hydrophobic PES membrane;prewetting the hydrophobic PES membrane in a sufficient amount of aliquid having a sufficiently low surface tension; exposing the wet PESmembrane to a sufficient amount of aqueous solution of oxidizer; andafter the exposing act, heating the hydrophobic PES membrane for asufficient time at a sufficient temperature.

Another aspect of the present disclosure includes a method ofmanufacturing hydrophilic polyethersulfone (PES) membrane comprising theacts of: providing hydrophobic PES membrane; prewetting the membrane inalcohol; washing the membrane with DI water; immersing the washedmembrane in an aqueous solution of about 2 to about 9% ammoniumpersulfate; heating the solution with the immersed membrane from ambienttemperature to about 80 to about 95° C. and then maintaining theresultant membrane at about 80° C. to about 95° C. for about 15 minutes;washing the membrane in water and then drying the resultant membrane.

Yet another aspect of the present disclosure includes a method ofmanufacturing hydrophilic polyethersulfone (PES) membrane comprising theacts of: providing hydrophobic PES membrane; prewetting the hydrophobicPES membrane in IPA; washing the resultant membrane with DI water; andimmersing the resultant membrane in about a 12% aqueous solution ofsodium hypochlorite for about 3 minutes at about 90° C. to about 95° C.

Still another aspect of the present disclosure includes a method ofmanufacturing hydrophilic PES membrane comprising the acts of: providinghydrophobic PES membrane; prewetting the hydrophobic PES membrane withabout a 50% aqueous solution of methanol; washing the resultant membranewith DI water; immersing the resultant membrane in about a 20% solutionof hydrogen peroxide (H₂O₂); heating the hydrogen peroxide (H₂O₂)solution at about 50° C. to about 70° C. for about 30 minutes; raisingthe temperature of the hydrogen peroxide (H₂O₂) solution to about 98°C.; maintaining the temperature of the hydrogen peroxide (H₂O₂) solutionat about 98° C. temperatures for about 40 minutes.

Another aspect of the present disclosure includes removing the membranefrom the hydrogen peroxide (H₂O₂) solution; washing the resultantmembrane with DI water for about 10 minutes at a temperature of about40° C.; and drying the resultant membrane at about 60° C. for about 40minutes.

Yet another aspect of the present disclosure includes during theimmersing act, using an aqueous solution containing about 71% DI water,about 15% hydrogen peroxide and about 4% APS.

Still another aspect of the present disclosure includes heating themembrane in the above aqueous solution at a temperature of about 50° C.to about 70° C. for about 30 minutes; uniformly raising the temperatureof the aqueous solution to about 92° C. for about 20 minutes; andthereafter, maintaining the temperature of the aqueous solution at about92° C. for about 20 minutes.

Another aspect of the present disclosure includes removing the resultantmembrane from the above aqueous solution; washing the resultant membranewith DI water for about 15 minutes at a temperature of about 40° C.; anddrying the resultant membrane at about 65° C. for about 35 minutes.

Another aspect of the present disclosure includes the use of gelmembrane which has gone through phase inversion and washing but has notbeen dried. Such “gel” membrane will be treated in a similar way asdescribed in this section

Another aspect of the present disclosure includes a method ofmanufacturing hydrophilic polyethersulfone (PES) membrane comprising theacts of: providing gel PES membrane; exposing the gel PES membrane to asufficient amount of an aqueous solution of oxidizer; and after theexposing act, heating the hydrophobic PES membrane for a sufficient timeat a sufficient temperature.

Still another aspect of the present disclosure includes after theexposing act in the solution of oxidizer, operatively positioning themembrane between two films so that the membrane is sandwichedtherebetween; and continuously moving the sandwiched membrane through atlest one heating zone.

Yet another aspect of the present disclosure includes during the heatingact, operatively positioning the membrane in a saturated water steammedium; and continuously moving the membrane through the saturated watersteam medium.

Other objects and advantages of the disclosure will be apparent from thefollowing description, the accompanying drawings and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a typical representative priorart system for PES membrane coating to produce a hydrophilic PESmembrane;

FIG. 2 is a schematic representation of a representative dry membranebatch process system for the hydrophilization process of PES membraneaccording to the present disclosure;

FIG. 3 is a schematic representation of a laboratory system for membraneoxidation using a sandwich method;

FIG. 4A is a schematic representation of a representative method ofheating uncovered, unsupported membrane in a steam medium;

FIG. 4B is a schematic representation of a representative method ofheating uncovered membrane on a transporting belt in a steam medium;

FIG. 4C is a schematic representation of a representative method ofheating uncovered membrane on a rotating drum in a steam medium;

FIG. 5 is a schematic representation of a representative method ofoxidizing uncovered “gel” membrane;

FIG. 6 illustrates protein binding results for various membranes; and

FIG. 7 is a schematic representation of a representative method of arepresentative two-cycle process of PES membrane oxidation.

DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

The present disclosure is directed to a new effective and economicalmethod for the hydrophilization of PES membrane, which can successfullycompete with all previously known methods and, quite possibly, exceedthem.

We found that PES membrane hydrophilization was effectively andeconomically performed by utilizing a chemical oxidation process withoututilization of complicated equipment, such as, for example, plasmatreatment reactors and we believe this chemical oxidation process can besuccessfully applied in industrial conditions for commercial membranemanufacturing including continuous manufacturing processes.

The following examples describe the hydrophilization of PES membraneusing oxidation with ammonium persulfate, and other representativeoxidation agents according to the present disclosure.

Unless otherwise indicated, all numbers expressing quantities ofingredients, properties such as molecular weight, reaction conditions,and so forth used in the specification and claims are to be understoodas being modified in all instances by the term “about.” Accordingly,unless indicated to the contrary, the numerical parameters set forth inthe following specification and attached claims are approximations thatmay vary depending upon the desired properties sought to be obtained bythe present disclosure. At the very least, and not as an attempt tolimit the application of the doctrine of equivalents to the scope of theclaims, each numerical parameter should at least be construed in lightof the number of reported significant digits and by applying ordinaryrounding techniques.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contain certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements.

We performed the PES membrane oxidation to achieve PES membranehydrophilization by treating the hydrophobic PES membrane in an aqueoussolution of an oxidizer.

One representative oxidizer, Ammonium persulfate (NH₄)₂S₂O₈, was chosenas the oxidizer for initial use in this process.

Ammonium persulfate (APS) is known to be a strong water solubleoxidizer: its standard oxidation potential is 2.01 volts. According tothis potential APS is placed near the top of the oxidizers list.

In the following table, the standard oxidation potentials for theseveral popular oxidizers are presented:

Oxidizer E°/V APS 2.01 Hydrogen peroxide (H₂O₂) 1.78 Bleach (HClO) 1.61Permanganate (MnO₄ ⁻) 1.5 Ozone (O₃) 1.24 Dichromate (Cr₂O₈ ⁻²) 1.23(The data are taken from the Handbook of Chemistry and Physics, CRCPress, 2003, page 8-28)

It is presently believed that, in an acid environment of pH<7.0, theincrease concentration of hydrogen ions (H⁺) may react with theoxidizing agent to generate a greater oxidation potential than in aneutral or base environment.

EXAMPLE 1

Example 1 illustrates the batch method of one process of the presentdisclosure.

The first step involves the: preparation of hydrophobic PES membrane.First, the membrane was cast on the glass plate using the dope offollowing formulation:

PES polymer (Radel polymer from Solvay) 14%; 1-Methyl-2-pyrrolidone(solvent) 21%; Polyethylene glycol 400 (poroformer) 65%.

Next, the cast membrane was air quenched inside a humidity chamber at atemperature of about 23° C. and having an air humidity from about 65 toabout 68% for about 25 minutes. The thus quenched membrane was thenwashed with DI water for about 30 minutes and then dried at about 80° C.for about 15 minutes.

The hydrophobic PES membrane, obtained as described above, was firstused in the present Example and was also used in other Examples(Examples 2-5 below).

Once the hydrophobic PES membrane was obtained, it was hydrophilized asfollows:

A sample of hydrophobic PES membrane (about 10 cm×about 10 cm) wasprewetted in isopropyl alcohol (IPA), washed with DI water and immersedin an aqueous solution of oxidizer (ammonium persulfate). Theconcentration of ammonium persulfate (APS) was about 3%. The solutionwas heated from ambient to about 90° C.-95° C. and maintained at about90° C.-95° C. for about 15 minutes.

After undergoing the above described treatment, the resultant membranewas cooled to ambient temperature, washed with water for about 10 toabout 20 minutes in order to remove the remains of oxidizer and thendried at about 70° C. for about 40 minutes.

The hydrophilic properties of membrane resulting from the above processare shown in the Table 1.

TABLE 1 Hydrophilic properties of membrane oxidized using a batchmethod. Wetting time Membranes in water Original PES membraneHydrophobic Oxidized membrane Instantaneously* Oxidized membrane afterboiling in water for 1 hour Instantaneously Oxidized membrane afterboiling in IPA for 1 hour Instantaneously *The term “Instantaneously”means that the wetting time was less than the time that could bemeasured using a stop-watch (normally less than 0.5 sec.).

As evident from the above, the resultant membrane readily demonstratedhydrophilicity and retained hydrophilicity upon exposure to boilingwater and IPA.

Example 2 demonstrates the membrane hydrophilization process utilizinganother oxidizer—Sodium Hypochlorite.

EXAMPLE 2

A sample of hydrophobic PES membrane (about 8 cm×40 cm) was prewetted inIPA, washed with DI water and immersed in about 12% aqueous solution ofsodium hypochlorite for about 3 minutes. Then the membrane was taken outof the solution and wound into a roll with diameter of about 3 cm. Therolled membrane was again immersed in 12% aqueous solution of sodiumhypochlorite, and the solution temperature was raised to about 97° C.The membrane was kept in the solution at this temperature for about 1hour. Then the membrane roll was taken out of the solution, the membranewas unwound, washed with DI water for about 30 minutes and dried atabout 70° C. for about 30 min. The resultant membrane was hydrophilic:it was wetted in water instantaneously.

Thus, the hydrophilization process of the PES membrane, performed asshown in examples 1 and 2, in accordance with the present disclosure, issimple, and can be applied in manufacturing conditions for the batchprocess of membrane treatment in the rolls, as shown in FIG. 2.

As shown in FIG. 2, the hydrophobic PES membrane 30 is prewetted inalcohol solution 32, then washed in water 33, and soaked in aqueoussolution of oxidizer at 34 and wound on the roll 35. The roll 35 isheated in the oven 36 (other heating methods are also possible, forexample, microwave heating and other known processes) to the temperatureof oxidation reaction for a sufficient time and is then the oxidizedmembrane 37 is processed through the washing 38 and drying 39 steps.

It is known that the continuous methods of membrane treatment arepreferable for manufacturing conditions because, as a rule, thecontinuous methods of membrane treatment are more economical and providebetter uniformity of produced membrane than batch methods.

Building on the success of the above examples 1 and 2, we furtherdeveloped a continuous method of manufacturing for PES membranehydrophilization production. In this particular representative method, a“sandwich” method of membrane treatment was used similar to thatutilized in the membrane coating manufacturing process of FIG. 1.

In this presently preferred manufacturing process, the membranecontinuously travels through the bath with alcohol for prewetting, thenpasses the water bath for washing, then passes the bath with APSsolution and, after soaking in APS solution, the membrane is sandwichedbetween the films (preferably Mylar films). The heat treatment of themembrane is performed continuously between the Mylar films, for exampleby moving the “sandwich” along the surface of the hot plate, preheatedto about 95-105° C. After the oxidation reaction is completed, themembrane is going out of Mylar films and then is washed and dried.

The specific process developed utilizing one possible “sandwich” methodfor membrane oxidation is described in the following Example, whichdescribes the presently preferred continuous manufacturing process forPES membrane hydrophilization production.

EXAMPLE 3

A sample of hydrophobic PES membrane (about 8 cm×about 24 cm) wasprewetted with IPA, washed with DI water for about 5 minutes and soakedin about 3% APS solution for about 2 minutes. Next, the sample wastreated in the device, shown in the FIG. 3. The membrane sample 45,after soaking in APS solution, was sandwiched between two bars of Mylarfilm 46. One end of the sandwich was connected to the roller 49, whichpulled the sandwich at a speed of about 30 cm/min along the surface of ahot plate 47. The hot plate had a temperature regulation +/−1° C. andwas preheated to about 102° C. A piece of sponge 48 was placed on thesandwich surface to uniformly press the sandwich to the hot plate andalso to prevent the membrane from cooling. The hot plate length wasabout 60 cm, and the speed of sandwich movement (about 30 cm/min)provided membrane heating on the hot plate for about 2 minutes. Afterheating, the membrane was taken out of the sandwich, washed in water forabout 10 minutes, and dried at about 80° C. for about 30 minutes.

As shown in Table 2, test A, the treated membrane was instantaneouslywetted in water and in NaCl solution having a concentration of about20%. The membrane retained hydrophilicity after heating in water in anautoclave at about 124° C. for about 1 hour.

Because of the short oxidation time (about 2 minutes), the “sandwich”method can potentially be conveniently arranged as a continuous processfor the large-scale manufacturing of hydrophilic PES membrane.

During our study, we surprisingly found that we could successfullyhydrophilize membrane in the gel state using the oxidation process ofthe present disclosure. The gel membrane is a membrane precursor, whichwas gone through the stages of casting, quenching and washing, but hasnot been dried.

Oxidization of the membrane in the gel state is very interesting becausethe use of membrane in the gel state significantly shortened themanufacturing process of hydrophilic PES membrane suitable forcommercial scale processing. The use of the membrane in the gel stateapproach eliminated the step of membrane drying (after the phaseinversion and washing steps) as well as the steps of membrane prewettingwith IPA and washing IPA off the membrane resulting in the efficient andeffective method of manufacturing hydrophilic PES membrane suitable forcommercial scale processing.

The oxidation of the membrane in a gel state can have an additionaladvantage in that utilization of the gel membrane can significantlyincrease the efficiency of the oxidation process.

As known by those skilled in the art, membrane in the gel state has muchhigher porosity than a dried membrane. During the drying process, themembrane shrinks and, because of this shrinkage, it is believed that thenumber and the diameter of pores in the membrane can be significantlyreduced. Due to a developed system of pores, the gel membrane istherefore believed to be more penetratable for different dissolvedsubstances than for a dried membrane.

We presently believe that since the oxidizers utilized with the presentdisclosure can penetrate into the structure of gel membrane much fasterand deeper, significantly increased degree of oxidation andhydrophilicity can be achieved by oxidation of the membrane in a gelstate as compared to the oxidation of the previously dried membrane.

The presently preferred manufacturing process for PES membrane in a“gel” state is described below in the Example 4.

EXAMPLE 4

A sample of gel or “never dried” PES membrane (about 8 cm×about 20 cm)was soaked in APS solution, and treated the same way as described in theexample 2. The only difference was that because a “never dried” membranewas utilized, the step of membrane prewetting in alcohol and the step ofwashing off the alcohol were excluded. The hydrophilicity of theresulting membrane is shown in the Table 2, Test B.

As can be seen, the resultant membranes produced using both type ofsamples, previously dried membranes and the membranes in the gel form,showed high hydrophilicity. In an effort to simulate the membranesterilization process, the resultant membranes were subjected totreatment in an autoclave at about 124° C. In the end, thehydrophilicity of all samples tested was not noticeably changed. At thesame time, the process of hydrophilization of “gel” membrane issignificantly shorter since it does not include the operations of dryingmembrane after quenching and washing and the operations of membraneprewetting and washing before oxidation.

TABLE 2 Wetting time of PES membranes after oxidation using a sandwichmethod. Wetting time, sec. Test Membrane In water In 20% NaCl AMembrane, oxidized after drying Oxidized membrane withoutInstantaneously Instantaneously additional treatment Oxidized membrane,boiled in Instantaneously Instantaneously water for 1 hour Oxidizedmembrane heated in Instantaneously Instantaneously an autoclave at 124°C. for 45 min. B Membrane, oxidized in a gel state Oxidized membranewithout Instantaneously Instantaneously additional treatment Oxidizedmembrane, boiled in Instantaneously Instantaneously water for 1 hourOxidized membrane heated in Instantaneously Instantaneously an autoclaveat 124° C. for 45 min.

One possible economical disadvantage of utilizing the “sandwich” schemein the production process is the significant consumption of Mylar films.However, the application of liquid impermeable films, such as Mylar, inthe production process is necessary in order to prevent the PES membranefrom drying out while being treated at high temperature, such as, forexample, 80-95° C. Without a film cover, the membrane dries very fast onthe hot plate and thus, the oxidization reaction is insufficient toproduce hydrophilic membrane since APS can react with a membrane onlywhen the APS is in the dissolved state.

In our continuing efforts to simplify and economize the hydrophilic PESmembrane manufacturing process, we discovered a method of continuousmembrane hydrophilization that did not require the use of the Mylarfilms for membrane oxidation processing and is believed simpler than a“sandwich” method. To prevent drying of uncovered membrane during theoxidation reaction, we found that heating the membrane in the medium ofsaturated steam was sufficient to obtain and maintain the conditionsnecessary for the oxidation process to be completed without filmapplication.

It is known that the saturated water steam has the highest possiblehumidity at the certain temperature and cannot accept any additionalamount of water. Because of this at the conditions of our experiment,the saturated steam medium reliably prevents the membrane from drying.

The relatively low temperature of the oxidation process (below 100° C.)facilitates the application of a steam treatment process withoutpressure. At the above conditions, the process is safe and the requiredequipment is relatively simple and inexpensive, as compared to someprior art processes.

The following example illustrates the hydrophilization of uncoveredmembrane (without Mylar films being utilized in the process):

EXAMPLE 5

A sample of hydrophobic previously dried PES membrane about 5 cm×about 8cm (sample A) was prewetted in IPA, washed with water for about 10minutes and soaked in about 6% APS solution for about 5 minutes. Asample of hydrophobic “never dried” PES membrane about 5 cm×about 8 cm(sample B) was soaked in about 6% APS solution (without previousprewetting and washing). Both samples were placed on a piece on metallicnet (about 10 cm×about 10 cm). A 2 L beaker was filled with water toabout ¼ of its volume, and water was brought to boiling. The net withmembrane samples was fixed inside the beaker approximately at about 10cm above the water level. The beaker was covered, and after about 6minutes of exposure to the medium of saturated steam, the samples weretaken out, washed with water for about 10 minutes and dried at about 70°C. Both samples (obtained from a previously dried membrane and from a“gel” membrane) demonstrated high hydrophilicity, as shown in the Table3. As should be evident, both samples were instantaneously wetted inwater and in about 20% NaCl solution

At this point, a control process was undertaken which comprised thetreatment of the membrane samples without the application of the steammedium. As shown in sample C in Table 3 below, the hydrophobic,previously dried, PES membrane was prewetted, washed and soaked in APSsolution the same way as it is described in the Process for the sample Aand sample D of gel membrane was soaked in APS solution the same way asit is described in the Process for the sample B. Both samples (C and D)were placed without being placed between films on the surface of themetallic plate preheated to about 95° C. and then were heated on thisplate at about 95° C. for about 6 minutes. Then the samples were washedand dried the same way as it was described in the Process 1.

Table 3 below shows the hydrophilicity of the samples A, B, C and Dobtained in Example 5 below.

TABLE 3 Hydrophilicity of the samples, heated without films in the steammedium and without the steam medium. Sam- Wetting time ple Membrane Inwater In 20% NaCL Membranes heated in a steam medium A Membrane oxidizedafter drying: Oxidized membrane without Instantaneously Instantaneouslyadditional treatment Oxidized membrane boiled in InstantaneouslyInstantaneously water for 1 hour B Membrane oxidized in a gel state:Oxidized membrane without Instantaneously Instantaneously additionaltreatment Oxidized membrane boiled in Instantaneously Instantaneouslywater for 1 hour Membranes heated without steam medium C Membraneoxidized after drying: Not wettable Not wettable D Membrane oxidized ina Not wettable Not wettable gel state:

The results presented in the table 3 show that both types of membranes(previously dried and gel membranes), after hydrophilization in a steammedium obtained high and stable hydrophilicity. At the same time, themembranes, which were treated the same way but without application ofthe steam medium, were hydrophobic. It is believed that such membranesfailed to wet because the heating process allowed them to dry prior tocompletion of the oxidation reaction. These results clearly show theeffectiveness of the proposed method of oxidation of uncovered membranein the steam medium, according to the present disclosure.

Possible representative schemes for continuous membrane transportationthrough the steam chamber are shown in FIGS. 4A-C. The uncoveredmembrane 62 can pass the steam chamber 60 without support, asillustrated in FIG. 4A, or can be supported with a transporting belt 64,as illustrated in FIG. 4B. It is presently believed that the mostreliable way to transport the uncovered membrane through the steamchamber is on the surface of a hot rotating drum 68, as illustrated inFIG. 4C or on the surface of several successive drums.

FIG. 5 illustrates the presently preferred manufacturing method forhydrophilization of “gel” (never dried) membrane with application of thesteam medium. As illustrated in FIG. 5, this method is significantlyshorter and simpler than the previous traditional process of membranecoating, as illustrated in FIG. 1.

FIG. 5 shows a roll of “gel” membrane at 80. The membrane 80 isconnected to a rewind system (not shown). As the membrane 80 unwinds, ittraverses through the first station 82 where the membrane soaks inaqueous solution of APS. The APS concentration in the solution can be,for example, about 3% to about 6% by Wt., the temperature about 20-30°C., soaking time about 2-4 minutes. After leaving station 82, the thustreated membrane 80 traverses a second station 83 (steam chamber)wherein the membrane is heated with saturated water steam in accordancewith the diagram of FIG. 4 A or FIG. 4 B, or Figure C. The steamtemperature can be about 90° C. to about 98° C. and the time of membraneheating in the steam chamber can be about 2 to about 4 minutes. Afterundergoing treatment at the second station 83, the treated membranecontinues traversing to the third station at 84 (washing chamber)wherein the remains of oxidizer, which, possibly, can remain inside themembrane after the oxidation reaction is completed, are washed off withwater. After completing treatment at the third station 84, the membranecontinues to the fourth Station 85 (drier) wherein the membrane is driedat the temperature, for example, about 70 to about 80° C. for about 5 toabout 30 minutes. After drying at the station 85, the hydrophilizationprocess is accomplished and the hydrophilic PES membrane according tothe present disclosure is obtained.

In addition to the enhanced hydrophilic properties, the membranesproduced using the proposed method have low protein binding.

The protein binding test was performed using fluorescein tagged Goat IgGprotein (manufactured by Cedarlane Laboratories). The aqueous solutionof protein (with a protein concentration of about 10 μg/ml) was pumpedwith a syringe pump through a disk of tested membrane with a diameter ofabout 13 mm at the flow rate of about 1 ml/min. A concentration ofprotein in the influent and effluent was measured using a Perkin—Elmerluminescence spectrophotometer. The amount of protein adsorbed by themembrane was calculated by multiplying a volume of the protein solution,pumped through the membrane, by the difference between the proteinconcentrations in the influent and effluent. Several membranes weretested for comparison including the oxidized membranes obtained in theExample 1 and several commercial membranes with different proteinbinding.

FIG. 6 illustrates the protein binding results are presented in whereinthe Protein binding of different membranes are prepared according to thefollowing:

1-Millipore Durapore PVDF;

2-Membrana PES;

3-Millipore Express;

4-Sartorius Sartopore;

5-PES oxidized membrane;

6-Nylon SterASSURE.

FIG. 6 illustrates that the protein adsorption of the oxidized PESmembrane was close to the protein adsorption of the commercial membraneswith low protein binding (Millipore's PVDF membrane, Membrana PES;Millipore Express; Sartorius Sartopore) and was much lower than theprotein adsorption of the membrane with high protein binding (nylonmembrane). The obtained results show that the membrane, produced by theproposed hydrophilization method of the present disclosure, closelyapproximated the performance the group of those membranes known toexhibit low protein binding characteristics.

It is believed that the protein binding properties of oxidized PES canbe further improved with further optimization of the above describedprocess.

Prophetic Examples EXAMPLE 6

A sample of hydrophobic PES membrane (about 5 cm×about 10 cm) isprewetted into about a 50% aqueous solution of methanol, washed with DIwater and immersed in about a 20% solution of hydrogen peroxide (H₂O₂).The membrane is heated in the hydrogen peroxide (H₂O₂) solution at atemperature of about 50° C. to about 70° C. for about 30 minutes, thenthe temperature of the hydrogen peroxide (H₂O₂) solution is raised toabout 98° C. and is maintained at about 98° C. temperature for about 40minutes. Then, after the membrane is removed from the hydrogen peroxide(H₂O₂) solution, the membrane is washed with DI water for about 10minutes at a temperature of about 40° C. and dried at about 60° C. forabout 40 minutes.

While not wanting to be bound to any theory, it is presently believedthat the membrane oxidation process occurred at those conditions asfollows: after the first membrane heating (at about 50° C. to about 70°C.) step, the membrane oxidation process is believed to be mostlycompleted and the hydrogen peroxide concentration in the solution isdepleted. It is believed that the additional step of membrane heating atthe elevated temperature (at about 98° C.) is performed in order tofully complete the oxidation and to decompose the remaining H₂O₂. Sincethe products of H2O2 decomposition at the high temperature are water andoxygen, the resultant membrane, should not contain any hazardoussubstances.

EXAMPLE 7

A sample of hydrophobic PES membrane (about 5 cm×about 10 cm) isprewetted and washed the same way as it is described in example 6 above.The sample is immersed in an aqueous solution containing the followingingredients: about 71% DI water, about 15% hydrogen peroxide (the firstoxidizer) and about 4% APS (the second oxidizer). The membrane is heatedin the above aqueous solution at a temperature of about 50° C. to about70° C. for about 30 minutes. Then, the temperature of the aqueoussolution is presently preferably uniformly raised to about 92° C. forabout 20 minutes, after which, the temperature of the aqueous solutioncontaining the membrane is maintained at about 92° C. for about 20minutes. After removal from the above aqueous solution, the membrane iswashed with DI water for about 15 minutes at a temperature of about 40°C. and dried at about 65° C. for about 35 minutes.

While not wanting to be bound to any theory, it is presently believedthat the membrane oxidation process at those conditions appears toproceed as follows: during the first step of the process (at about 50°C. to about 70° C.) H₂O₂ functions as the only membrane oxidizer. APSdoes not appear to participate in the oxidation reaction since itsworking temperature is much higher (above 80° C.). After this first stepof the oxidizing process is completed, the temperature is raised toabout 92° C. and the second step of oxidation process is started, withAPS being included in the membrane oxidation.

It is presently believed that because of the multiple oxidationprocesses, the oxidation degree is believed higher, and the hydrophilicproperties of the oxidized membrane (including protein bindingproperties) are believed improved.

EXAMPLE 8

A sample of hydrophobic PES membrane (about 8 cm×about 24 cm) isprewetted with IPA, washed with DI water for about 5 minutes, and soakedin about a 20% solution of hydrogen peroxide. Then the sample issandwiched between two bars of Mylar film. The obtained sandwich ismoved along the surface of hot plates. The scheme of this process issimilar to the process shown in FIG. 3; the only difference is thatinstead of one hot plate (as it is shown in FIG. 3), two hot plates areused. The two hot plates have different temperatures with the first hotplate being preheated to a temperature of about 55° C. to about 75° C.,the second plate having a temperature of about 102° C. The length ofeach hot plate is about 60 cm; the speed of the sandwiched movement isabout 30 cm/min. The membrane is heated on each hot plate for about 2minutes.

It is believed that the membrane treatment described above according tothis scheme is approximately equal to the membrane treatment, asdescribed in the example 6, and the same explanation of the processadvantages applies.

During the heating of the first plate at about 50° C. to about 70° C.,the hydrogen peroxide concentration in the solution is depleted. Duringthe second cycle of heating (heating on the second plate at the hightemperature), all the remaining of H₂O₂ is decomposed. Since theproducts of H₂O_(2 decomposition) are water and oxygen, the resultantmembrane is not expected to contain any hazardous substances.

EXAMPLE 9

A sample of hydrophobic PES membrane (about 5 cm×50 cm) is prewetted andwashed the same way as described in the Example 6 above. This sample isplaced on the bar of the Mylar film with the width about 7 cm. and thelength about 4 meters. The ends of the sample are attached with thestaples to the supporting Mylar film.

The scheme of the laboratory system 90, which simulates a continuoushydrophilization process, is presented on the FIG. 7. The Mylar film 91with attached membrane sample 92 is pulled by the roller 93 and is goingthrough the bath 94, containing a solution of the first oxidizer, thenalong the steam chamber 95, then through a bath 96 with a solution ofthe second oxidizer, then along the steam chamber 97, and finally iswound on the roller 92.

The conditions of the oxidation process are as follows:

The solution of the first oxidizer: aqueous solution of bleach (HClO)with a concentration of about 12%; the solution of the second oxidizer:aqueous solution of APS with a concentration of about 6%. The speed ofthe Mylar film movement is about 20 cm/minute; the length of the steamchambers is about 50 cm.

After the membrane sample reaches the roller 92, it is detached from theMylar film, washed in water at about 40° C. to about 50° C. and dried atabout 65° C. for about 30 minutes.

It is presently believed that the first cycle of membrane oxidationutilizing the oxidizer with lower oxidation potential (bleach), works asa “pretreatment” for the final oxidation cycle with an application ofthe oxidizer with high oxidation potential (APS).

EXAMPLE 10

The membrane oxidation experiment is performed the same way as itdescribed in the Example 9, but the solution in the bath 94 is about 3%APS, and the solution in the bath 96 is about 6% APS.

It is presently believed that the resultant membrane, obtained after twooxidation cycles, will have a higher oxidation degree and higherhydrophilicity, compared to the membrane obtained after a singleoxidation cycle.

EXAMPLE 11

A sample of hydrophobic PES membrane (about 6 cm×about 6 cm) isprewetted into 50% aqueous solution of methanol and washed with DI waterand immersed in aqueous solution, which contains about 95.8% water,about 4% APS, and about 0.2% of water soluble complex of Cu(II)(oxidation catalyst).

As is known according to available data in published literature,complexes of transition metals, including, but not limited to copper,zinc, iron etc. are water soluble substances, can be employed ascatalysts for oxidation reactions and can significantly intensify theactivity of oxidizers. Such complexes of transition metals are believedto lower the actuation energy barrier.

The membrane is heated in the above described solution at a temperatureof about 70° C. for about 10 minutes, and then the membrane is removedfrom the solution, is washed with DI water for about 15 minutes at atemperature of about 40° C., and dried at about 70° C. for about 40minutes.

It is believed that the membrane oxidation process, performed in thepresence of the above described catalyst and any other catalyst havingsimilar properties, will provide the membrane with enhanced hydrophilicproperties, and reduced protein binding.

In view of the foregoing and in summary, there appear to be manypossible potential process variations as specifically described aboveand include but are not limited to:

1. A method of PES membrane hydrophilization by oxidation wherein adried membrane (the membrane has completed all the stages of themanufacturing process, including, but not limited to: casting, phaseinversion, washing and drying) is oxidized.

2. A method of PES membrane hydrophilization by oxidation wherein, inorder to make a hydrophilization process significantly simpler andshorter, a never dried gel membrane (the membrane after the stages ofcasting, phase inversion and washing, but prior to drying) is oxidized.

3. PES membrane hydrophilization by oxidation using rolls of themembrane in a batch process method of production.

4. PES membrane hydrophilization by oxidation using a continuous processwherein the membrane is sandwiched between Mylar films.

5. PES membrane hydrophilization by oxidation using a continuous processwithout the films application wherein uncovered membrane after soakingin the solution of the oxidizer is heated in a saturated steamenvironment in order to prevent membrane drying.

6. The method of PES membrane hydrophilization by oxidation described in4 above wherein the uncovered membrane traverses the steam chamberwithout support, or the uncovered membrane can be supported with atransporting belt, or the uncovered membrane can be transported on thesurface of the rotating drum or several successive drums.

7. The methods of PES membrane hydrophilization by oxidation describedin 1-5 above wherein the temperature of the membrane treatment ischanged during the oxidation process. This method is illustrated aboveby prophetic Example 6.

8. The methods of PES membrane hydrophilization by oxidation describedin 1-6 wherein a mixture of two or more different oxidizers is utilized.The oxidizers can have different working temperatures and can beassorted such that the temperature elevation provides desirablesequential processes in the membrane oxidation process of the presentdisclosure. This method is illustrated by prophetic Example 7 above.

9 The methods of PES membrane hydrophilization by oxidation described in6-7 wherein not one but several oxidization cycles are utilized. Theseoxidization cycles may be performed at different temperatures, differentoxidizers, different concentrations of oxidizers. Prophetic example 8above illustrates the utilization of two oxidation cycles performed atdifferent temperatures; prophetic example 9 above illustrates theutilization of two oxidation cycles performed with different oxidizers;prophetic example 10 above illustrates the utilization of two oxidationcycles performed at different concentrations of oxidizer.

10. The methods of PES membrane hydrophilization as described in 1-9above wherein the membrane oxidization is performed in the presence ofthe catalysts of the oxidation process, such as, for example, oxides orcomplexes of the transition metals, including, but not limited to, iron,copper, zinc, etc. The method is illustrated above by prophetic example11.

While the articles, apparatus and methods for making the articlescontained herein constitute presently preferred embodiments of theinvention, it is to be understood that the disclosure is not limited tothese precise articles, apparatus and methods, and that changes may bemade therein without departing from the scope of the disclosure, whichis defined in the appended claims.

1. A method of manufacturing hydrophilic polyethersulfone (PES) membranecomprising the acts of: providing hydrophobic PES membrane; prewettingthe hydrophobic PES membrane in an amount of a liquid having a lowsurface tension; exposing the wet hydrophobic PES membrane to an amountof an aqueous solution of oxidizer; after the exposing act, heating thehydrophobic PES membrane at a predetermined temperature; during theheating act, operatively positioning the PES membrane in a saturatedwater steam medium; and continuously moving the PES membrane through thesaturated water steam medium.
 2. The method of claim 1 furthercomprising the act of: after the prewetting act, washing the resultantmembrane with water.
 3. The method of claim 2 further comprising the actof: after the heating act, drying the resultant membrane.
 4. The methodof claim 3 wherein, during the drying act, the resultant membrane isexposed to heat of about 70° C. to about 95° C.
 5. The method of claim 3wherein the washing act is partly performed before the membraneoxidation act.
 6. The method of claim 2 wherein, during the heating actthe hydrophobic PES membrane is heated at about 90° C. to about 95° C.for about 15 minutes.
 7. The method of claim 1 wherein the oxidizer isselected from the group consisting of: Ammonium persulfate (NH4)2S2O8,Hydrogen peroxide (H2O2), Bleach (HClO), Permanganate (MnO4−), Ozone(O3) or Dichromate (Cr2O8 −2) and combinations thereof.
 8. The method ofclaim 1 wherein, during the heating act, the PES membrane is containedin a sufficient aqueous solution of sufficient oxidizer to causeoxidation of the membrane.
 9. The method of claim 1 further comprisingthe act of: after the heating act, washing the resultant membrane withwater for a sufficient time in order to sufficiently remove the remainsof the oxidizer therefrom.
 10. The method of claim 1 wherein, theoxidizer comprises: Ammonium persulfate (NH₄)₂S₂O₈.
 11. The method ofclaim 1 further comprising the acts of: after the exposing act in thesolution of oxidizer, operatively positioning the membrane between twofilms so that the membrane is sandwiched therebetween; and continuouslymoving the sandwiched membrane through at lest one heating zone.
 12. Amethod of manufacturing hydrophilic polyethersulfone (PES) membranecomprising the acts of: providing gel PES membrane; exposing the gel PESmembrane to an amount of an aqueous solution of oxidizer; after theexposing act, heating the hydrophobic PES membrane; during the heatingact, operatively positioning the PES membrane in a saturated water steammedium; and continuously moving the PES membrane through the saturatedwater steam medium.
 13. The method of claim 12 wherein the oxidizer isselected from the group consisting of: Ammonium persulfate (NH₄)₂S₂O₈,Hydrogen peroxide (H₂O₂), Bleach (HClO), Permanganate (MnO₄ ⁻), Ozone(O₃) or Dichromate (Cr₂ O₈ ⁻²) and combinations thereof.
 14. The methodof claim 12 further comprising the acts of: after the exposing act inthe solution of oxidizer, operatively positioning the membrane betweentwo films so that the membrane is sandwiched therebetween; andcontinuously moving the sandwiched membrane through at lest one heatingzone.